线程

什么是线程？

　　进程：资源单位

　　线程：执行单位

　　每一个进程中都默认有一个线程（称之为主线程）

为什么要用线程？

　　开一个进程：

　　　　需要申请内存空间　　耗时

　　　　将代码拷贝到申请的内存空间中　　耗时

　　开线程：

　　　　不需要申请内存空间

　　开线程的开销比开进程的开销小

如何使用线程？

一、开启线程的两种方式（和进程差不多相似）

from threading import Thread
import time
def task(name):
    print('%s is running'% name)
    time.sleep(1)
    print('%s is over'% name)
if __name__ == '__main__':
    t = Thread(target=task,args=('egon',))
    t.start()
    print('主')
输出：

egon is running
主
egon is over

方式二：

from threading import Thread
import time
class Mythred(Thread):
    def __init__(self,name):
        super().__init__()
        self.name = name
    def run(self):
        print('%s is running'% self.name)
        time.sleep(1)
        print('%s is over' %self.name)
if __name__ == '__main__':
    t = Mythred('tank')
    t.start()
    print('主')
输出：

egon is running
主
egon is over

二、join方法（优先加载子线程）

from threading import Thread
import time
def task(name):
    print('%s is running' %name)
    time.sleep(1)
    print('%s is over'%name)
if __name__ == '__main__':
    t = Thread(target=task,args=('geon',))
    t.start()
    t.join()
    print('主')
输出：
egon is running
egon is over
主

三、线程之间内存空间相互隔离

from threading import Thread
import time
x = 100
def tash():
    global x
    print(x)
    time.sleep(1)
    x = 6000
    print(x)
t = Thread(target=tash)
t.start()
t.join()
print(x)
输出：
100
6000
100

四、线程对象的其它属性
# active_count 返回当前活动链接数
# current_thread().name 获取当前线程的名字

from threading import Thread,active_count,current_thread
import os
import time
def task(name):
    print('%s is running' %name,current_thread().name)　　#当前线程的名字
    time.sleep(1)
    print('%s is over' %name)

def info(name):
    print('%s is running' %name,current_thread().getName())　　#当前线程的名字另外一种表示方法
    time.sleep(1)
    print('%s is over' %name)
t = Thread(target=task,args=('xxx',))
t1 = Thread(target=info,args=('xxx',))
t.start()
t1.start()
print(active_count()) # 查看存活的线程数
print(os.getpid())　　# 查看线程id
print(current_thread().name)　　#查看线程的名字（主线程MainThread）
输出结果：

xxx is running Thread-1
xxx is running Thread-2
3
14996
MainThread
xxx is over
xxx is over

五、守护线程

from threading import Thread
import time


def task(name):
    print('%s is running'%name)
    time.sleep(1)
    print('%s is over'%name)

if __name__ == '__main__':
    t = Thread(target=task,args=('xxx',))
    t.daemon = True　　# 守护线程
    t.start()
    print('主')
输出：
　　xxx is running
　　主

六、互斥锁

from threading import Thread,Lock
import time
import random
mutex = Lock()
n = 100
def task():
    global n
    mutex.acquire()　　# 锁定
    tmp = n
    time.sleep(0.1)
    n = tmp -1
    mutex.release()　　#解锁
t_list = []

for i in range(100):
    t = Thread(target=task)
    t.start()
    t_list.append(t)

for t in t_list:
    t.join()

print(n)
输出：
0